Trim the meat of any excess fat, and season well with salt and pepper. Heat olive oil in a large skillet over medium-high heat. Place the meat in the hot skillet, and sear it quickly on all sides.
Transfer the meat to a slow cooker and top it with the chopped onion. Season with chopped green chiles, chili powder, cumin, garlic powder, & hot pepper sauce.
Cover, and cook on low for 8 hours or until meat is tender & falling apart, checking to make sure there is always at least a small amount of liquid in the bottom of the cooker (add more liquid if need be).
Transfer the meat to a bowl and shred it using two forks.